A blacklist and IP-address database, formerly privately owned but now part of the email vendor Ironport. Many ISPs check the IP addresses of incoming email against Spamcop’s records to determine whether the address has been blacklisted due to spam complaints.

The 3 Things To Avoid When Emailing Your List
When you decide to have an opt-in list, it is not just a matter of sending your subscribers your promotional newsletters or catalogs.